JP2011077932A - Image processing apparatus, and image processing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a technology for generating subframe images to reduce lightness/darkness for a reproduction result even if the subframe images generated by frame rate conversion are reproduced. <P>SOLUTION: A frame rate converting unit 101 generates a plurality of subframe images from a captured frame image. Gradation converting units 102, 103 perform gradation conversion on the subframe images. A switching unit 104 sequentially outputs the subframe images on which the gradation conversion has been performed by the gradation converting units 102, 103. In the gradation conversion, the same gradation conversion is applied to a pixel whose luminance value is smaller than or equal to a threshold in each of the subframe images, and different gradation conversion is applied to each of the subframe images for a pixel having a luminance value larger than the threshold. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a frame rate conversion technique.

  The video standard SMPTE-170M (commonly known as NTSC) defines a video display frequency of 60 Hz. This video is standardized in broadcasting and imaging systems in Japan, Korea, and Latin America, mainly in the standardized US. The display frequency is adopted. On the other hand, video display at a higher drive frequency is possible with the improvement of the technology of the display panel / drive circuit, and in fact, a technology of driving at a double speed of 120 Hz or a quadruple speed of 240 Hz has appeared.

  For example, Patent Document 1 proposes a technique that increases the frame frequency of a display image and suppresses a decrease in spatial frequency characteristics that causes motion blur. On the other hand, Non-Patent Document 1 reports a perceptual sensitivity relationship between the light emission driving frequency and the brightness. In this report, the result of investigating the difference in brightness between blinking light and steady light is reported. According to the result of the subject experiment of Non-Patent Document 1, when the physical emission intensity per unit time is the same, the blinking light feels brighter than the steady light when the frequency of the blinking light is about 70 Hz or less, and about 80 Hz or more. Reported that the blinking light and the steady-state light have the same brightness.

JP 2001-42831 A

Morimine, “Effects of blinking stimuli above the critical fusion frequency on brightness perception”, Journal of the Institute of Image Information and Television Engineers, Vol. 52, no. 4, pp. 612-615

  For an input frame of 60 Hz, when the subframe is generated so that the emission intensity per unit time is the same and doubles to 120 Hz or quadruple 240 Hz, and displayed by, for example, impulse driving, it depends on the driving frequency as described above. The perception sensitivity of human brightness is different. Therefore, there is a problem that the brightness perceived by humans becomes darker than when displaying at 60 Hz.

  The present invention has been made in view of the above problems, and each sub-frame image is reduced so that the brightness and darkness of the reproduction result can be reduced even when each sub-frame image generated by frame rate conversion is reproduced. It aims at providing the technology for generating.

  In order to achieve the object of the present invention, for example, an image processing apparatus of the present invention comprises the following arrangement. That is, an acquisition unit that sequentially acquires a plurality of frame images, a generation unit that generates a plurality of subframe images from the frame images acquired by the acquisition unit, and a conversion that performs gradation conversion on each of the plurality of subframe images And means for sequentially outputting each subframe image subjected to gradation conversion by the conversion means, the conversion means for each pixel having a luminance value equal to or less than a threshold value in each subframe image. Are subjected to the same gradation conversion, and in each subframe image, different gradation conversions are performed in the respective subframe images for pixels whose luminance value is larger than the threshold value.

  According to the configuration of the present invention, even when each subframe image generated by frame rate conversion is reproduced, each subframe image can be generated so that the contrast with respect to the reproduction result is reduced.

(A)-(c) is a block diagram which shows the function structural example of an image processing apparatus. The flowchart of the process performed with respect to one frame image. (A), (b), (e), (f) is a figure which shows the conversion characteristic of gradation conversion, (c), (d) is a figure which shows the conversion curve of gradation conversion. The flowchart of the process performed with respect to one frame image. The figure for demonstrating the minimum value filter process by the minimum value filter part. The figure explaining each sub-frame image. (A) is a flowchart of the process with respect to 1 frame image, (b) is a flowchart which shows the detail of the process in step S303. (A), (b) is a figure explaining each sub-frame image, (c) is a figure which shows a synthetic | combination display brightness | luminance. FIG. 3 is a diagram illustrating a configuration example when the image processing apparatus according to the first embodiment is extended. FIG. 3 is a block diagram illustrating an example of a functional configuration of the image processing apparatus. The block diagram which shows the structural example of the hardware of a computer. The figure which shows the structural example of the apparatus of the application object of an image processing apparatus.

  Preferred embodiments of the present invention will be described below with reference to the accompanying drawings. The embodiment described below shows an example when the present invention is specifically implemented, and is one of the specific examples of the configurations described in the claims. Further, in the following description, the brightness perceived by the person including the effect of increasing the brightness perceived by the person with respect to the physical light emission intensity is referred to as “feeling of brightness”.

[First Embodiment]
An image processing apparatus that performs frame rate conversion on an input frame image so as to appear brighter in a high luminance portion with respect to physically equal emission intensity will be described below. FIG. 1A is a block diagram illustrating a functional configuration example of the image processing apparatus according to the present embodiment. As shown in FIG. 1A, the image processing apparatus according to the present embodiment includes a frame rate conversion unit 101 (shown as FRC 101 in FIG. 1A), a gradation conversion unit 102, a gradation conversion unit 103, A switching unit 104.

  A plurality of frame images are sequentially input (sequentially acquired) to the frame rate conversion unit 101. The frame rate conversion unit 101 generates a plurality of subframe images having different gradations from the input frame image. In the present embodiment, as an example, a case where two subframe images having different gradations are generated from one frame image will be described. Then, the frame rate conversion unit 101 transmits the generated one subframe image to the gradation conversion unit 102, and transmits the generated other subframe image to the gradation conversion unit 103. Therefore, when the frame rate conversion unit 101 generates N subframe images from one frame image, the gradation conversion unit needs to prepare the number of subframe images to be generated, that is, N.

  Each of the gradation conversion units 102 and 103 performs gradation conversion of the input subframe image. More specifically, each of the gradation conversion units 102 and 103 performs the same gradation conversion for pixels whose luminance value is less than or equal to the threshold value, but for pixels whose luminance value is larger than the threshold value, Different gradation conversions are performed by the gradation conversion units 102 and 103.

  The switching unit 104 sequentially selects and outputs the subframe images that have been subjected to the tone conversion by the tone conversion unit 102 and the tone conversion unit 103 to the outside. Note that there is no particular limitation on which of the gradation conversion unit 102 and the gradation conversion unit 103 is selected first.

  As shown in FIG. 12, the image processing apparatus according to the present embodiment processes a frame image (video signal) input via the video signal conversion unit 1801 and the image processing unit 1802, and displays the frame image via the drive circuit 1803. It is incorporated so as to be sent to the panel 1804. FIG. 12 is a diagram illustrating a configuration example of an apparatus to which the image processing apparatus according to the present embodiment is applied.

  FIG. 2 is a flowchart of processing performed on one frame image by the image processing apparatus according to the present embodiment. First, in step S102, the frame rate conversion unit 101 acquires one frame image as an input frame image 201 (input image).

  Next, in step S <b> 103, the frame rate conversion unit 101 generates two subframe images 202 and 204 having different gradations from the input frame image 201. The frame rate conversion unit 101 transmits the generated subframe image 202 to the gradation conversion unit 102 and transmits the generated subframe image 204 to the gradation conversion unit 103.

  The method for generating a plurality of subframe images from the input frame image 201 is not particularly limited. For example, a plurality of input frame images 201 may be copied and each may be used as a subframe image, or a plurality of motion compensated intermediate images are generated as subframe images using the input frame image 201 and the previous frame image. You may do it. When generating a motion compensated intermediate image, for example, a method for performing a vector search as disclosed in JP-A-2005-301619 may be used.

  Next, in step S <b> 104, when the gradation conversion unit 102 acquires the subframe image 202 from the frame rate conversion unit 101, gradation conversion is performed on the subframe image 202 to generate a subframe image 203. Similarly, when the gradation conversion unit 103 acquires the subframe image 204 from the frame rate conversion unit 101, the gradation conversion unit 103 performs gradation conversion on the subframe image 204 to generate a subframe image 205.

  Here, the gradation conversion performed by each of the gradation conversion unit 102 and the gradation conversion unit 103 will be described. 3A and 3B are diagrams showing the conversion characteristics of gradation conversion performed by the gradation conversion unit 102 and the gradation conversion unit 103, respectively.

  3A shows the conversion characteristics in the gradation conversion performed by the gradation conversion unit 102, and FIG. 3B shows the conversion characteristics in the gradation conversion performed by the gradation conversion unit 103. ing. In FIG. 3A, the horizontal axis represents the input luminance value (input x), and the vertical axis represents the output luminance value (output f1). On the other hand, in FIG. 3B, the horizontal axis represents the input luminance value (input x) and the vertical axis represents the output luminance value (output f2).

  As described above, the gradation conversion unit 102 performs gradation conversion of the subframe image 202 based on the conversion characteristics shown in FIG. Therefore, the gradation conversion unit 102 calculates a new luminance value f1 (x) according to the following formula (conversion information) for a pixel having a luminance value x equal to or smaller than the threshold S1 in the subframe image 202.

f1 (x) = a × x
On the other hand, as described above, the gradation conversion unit 103 performs gradation conversion of the subframe image 202 based on the conversion characteristics shown in FIG. Therefore, the gradation conversion unit 103 calculates a new luminance value f2 (x) according to the following equation (conversion information) for a pixel having a luminance value x equal to or less than the threshold S1 in the subframe image 204.

f2 (x) = a × x (a is a coefficient)
Thereby, in any of the sub-frame images 202 and 204, the luminance value is updated based on the same conversion formula for the pixel having the luminance value x equal to or less than the threshold value S1. Further, the gradation conversion unit 102 calculates a new luminance value f1 (x) according to the following equation (conversion information) for a pixel having a luminance value x greater than the threshold value S1 in the subframe image 202.

f1 (x) = b × x + S1 × (ab) (b is a coefficient)
Also, the gradation conversion unit 103 calculates a new luminance value f2 (x) according to the following equation (conversion information) for a pixel having a luminance value x greater than the threshold value S1 in the subframe image 204.

f2 (x) = S1 × a
Thus, the luminance values of the sub-frame images 202 and 204 are updated based on different conversion formulas for the pixels having the luminance value x larger than the threshold value S1. That is, it can be said that the conversion information described above is information configured as follows. That is, when the input luminance value is less than or equal to the threshold value, the change rate of the output luminance value with respect to the input luminance value is configured to be the same for all the subframe images. Are different in all sub-frame images.

  In this way, the luminance value of each pixel is updated for both of the subframe images 202 and 204, and the subframe images 203 and 205 are generated. Returning to FIG. 2, in step S <b> 105, the switching unit 104 sequentially selects the subframe image 203 generated by the gradation conversion unit 102 and the subframe image 205 generated by the gradation conversion unit 103. The output frame image 206 is sent to the outside.

  FIGS. 8A and 8B are diagrams illustrating each sub-frame image when a frame image is input to the apparatus at 60 Hz and is output at 120 Hz. In each subframe image, a pixel group having a luminance value equal to or less than the threshold value S1 is output with an equal luminance value in each subframe image, as shown in FIG. On the other hand, in each sub-frame image, as shown in FIG. 8B, a difference occurs between the sub-frame images for the pixel group whose luminance value is larger than the threshold value S1, and the time frequency is 120 Hz and 60 Hz mixed. . This 60 Hz component has an effect of improving the feeling of brightness, and allows a person to recognize a pixel group having a luminance value larger than the threshold value S1 brightly.

[Second Embodiment]
In each embodiment described below, only a different part from the first embodiment will be described. In the present embodiment, the difference in brightness between the sub-frame images is given only to an isolated region having a high luminance value in the input frame image, thereby improving the feeling of brightness while suppressing large screen flicker.

  FIG. 1B is a block diagram illustrating a functional configuration example of the image processing apparatus according to the present embodiment. In FIG. 1B, the same components as those in FIG. 1A are denoted by the same reference numerals, and the description thereof is omitted.

  As described in the first embodiment, the frame rate conversion unit 101 generates a plurality of subframe images from the input frame image. In the present embodiment, as in the first embodiment, a case where two subframe images are generated from one frame image will be described. One subframe image 202 is input to the subtractor 108, and the other subframe image 204 is input to the minimum value filter unit 107.

  The minimum value filter unit 107 performs a known minimum value filter on the input subframe image 204 to generate a converted (processed) subframe image 213. The gradation conversion unit 103 performs gradation conversion on the subframe image 213 that has been converted by the minimum value filter unit 107 to generate a subframe image 205. The minimum value filter expands the minimum value in the filter size to all the pixels in the filter size. However, such a region expansion filter is not limited to the minimum value. For example, if there is an extreme minimum value in the filter size, this minimum value has a high possibility of noise, so the next smallest value after the minimum value is regarded as the minimum value and all pixels in the filter size are considered. You may extend to.

  The subtractor 108 generates a difference frame image 290 between the subframe image 202 input from the frame rate conversion unit 101 and the subframe image 205 input from the gradation conversion unit 103. The switching unit 104 sequentially outputs the difference frame image 290 generated by the subtractor 108 and the subframe image 205 that has been subjected to gradation conversion by the gradation conversion unit 103.

  FIG. 4 is a flowchart of processing performed on one frame image by the image processing apparatus according to the present embodiment. First, in step S202, the frame rate conversion unit 101 acquires one frame image as an input frame image 201 (input image).

  Next, in step S <b> 203, the frame rate conversion unit 101 generates two subframe images 202 and 204 from the input frame image 201. This generation method is not particularly limited, and may be the same as in the first embodiment. The frame rate conversion unit 101 sends the generated subframe image 202 to the subtractor 108 and sends the generated subframe image 204 to the minimum value filter unit 107.

  Next, in step S <b> 204, the minimum value filter unit 107 performs minimum value filter processing on the subframe image 204. Here, the minimum value filtering process will be described. Such a technique is well known and will be briefly described here. The minimum value filtering process is to perform the following conversion on the pixel value (luminance value) sx of each pixel constituting the image.

f (sx) = sx (sx ≦ S1)
f (sx) = s_min (sx> S1)
In such conversion, if the pixel value sx of the pixel of interest is equal to or less than the threshold S1, the pixel value sx is used as it is as the pixel value after conversion for the pixel of interest. On the other hand, when the pixel value sx is larger than the threshold value S1, the minimum pixel value s_min is acquired from the pixel values of the respective pixels in the area of the specified area centered on the target pixel, and the acquired pixel value s_min Is the pixel value after conversion for the pixel of interest.

  FIG. 5 is a diagram for explaining the minimum value filter processing by the minimum value filter unit 107. FIG. 5A shows the luminance value of each pixel before conversion, and FIG. The luminance value of each pixel after conversion is shown. In FIG. 5, the horizontal axis indicates the position of each pixel in one image, and the vertical axis indicates the luminance value of each pixel. In FIG. 5A, xv indicates a region (high luminance region) composed of pixels having a luminance value larger than the threshold value S1. When the minimum value filtering process is performed on the frame image having the luminance distribution shown in FIG. 5A, the luminance value in the high luminance region is converted into the minimum luminance value around it as shown in FIG. 5B. Has been.

  Returning to FIG. 4, in step S <b> 205, the gradation conversion unit 103 performs gradation conversion processing on the subframe image 213 that has been converted by the minimum value filter unit 107. Such gradation conversion processing is the same as that performed by the gradation conversion unit 103 in the first embodiment.

  Next, in step S206, the subtractor 108 generates a difference frame image 290 obtained by subtracting the subframe image 205 that has been subjected to gradation conversion by the gradation conversion unit 103 from the subframe image 202 received from the frame rate conversion unit 101. To do.

  Next, in step S207, the switching unit 104 sequentially selects the subframe image 205 generated by the gradation conversion unit 103 and the difference frame image 290 generated by the subtractor 108, and sends them as an output frame image 206 to the outside. To do.

  FIG. 6 is a diagram illustrating each sub-frame image when a frame image is input to the apparatus at 60 Hz and is output at 120 Hz. FIG. 6A shows an example of the input frame image 201. Since the area A and the area B are high-luminance areas, and the area of the area A is sufficiently larger than the area of the area B, even if the input frame image 201 is subjected to minimum value filtering, Although the luminance value is suppressed, the luminance value in the region A is not significantly suppressed. In the area B, as shown in FIG. In the area A, as shown in FIG. 6B, flicker is suppressed.

  As described above, according to the present embodiment, the gradation of the sub-frame image is controlled according to the luminance and area of the input frame image, and the brightness is increased by adding a difference between the sub-frame images only in an isolated region. The feeling of feeling can be improved, and flicker can be suppressed in other areas.

[Third Embodiment]
In the present embodiment, the frame rate conversion is performed so that the high luminance part looks brighter with respect to the physical maximum emission intensity. FIG. 1C is a block diagram illustrating a functional configuration example of the image processing apparatus according to the present embodiment. The configuration shown in FIG. 1C is a configuration in which a conversion gradation control unit 900 is added to the configuration shown in FIG. 1A, and the operations of the other units are the same as those in the first embodiment. It is.

  The conversion gradation control unit 900 analyzes the input frame image 201 to obtain a conversion characteristic (curve) f1 used by the gradation conversion unit 102 and a conversion characteristic (curve) f2 used by the gradation conversion unit 103, and obtains f1, f2 is set in the gradation conversion unit 102 and the gradation conversion unit 103, respectively.

  FIG. 7A is a flowchart of processing performed on one frame image by the image processing apparatus according to the present embodiment. In step S302, the conversion gradation control unit 900 acquires the input frame image 201. Next, in step S303, the conversion gradation control unit 900 analyzes the acquired input frame image 201 and obtains a conversion curve f1 used by the gradation conversion unit 102 and a conversion curve f2 used by the gradation conversion unit 103. Details of the processing in step S303 will be described later.

  Next, in step S304, the frame rate conversion unit 101 acquires the input frame image 201 via the conversion gradation control unit 900. Then, the frame rate conversion unit 101 generates two subframe images 202 and 204 having different gradations from the input frame image 201 in the same manner as in the first embodiment. The frame rate conversion unit 101 transmits the generated subframe image 202 to the gradation conversion unit 102 and transmits the generated subframe image 204 to the gradation conversion unit 103.

  In step S <b> 305, the gradation conversion unit 102 performs gradation conversion on the subframe image 202 acquired from the frame rate conversion unit 101 using the conversion curve f <b> 1 obtained by the conversion gradation control unit 900 to obtain a subframe image. 203 is generated. Similarly, the gradation conversion unit 103 performs gradation conversion on the subframe image 204 acquired from the frame rate conversion unit 101 using the conversion curve f2 obtained by the conversion gradation control unit 900, and the subframe image 205 is generated.

  Next, in step S306, the switching unit 104 sequentially selects the subframe image 203 generated by the gradation conversion unit 102 and the subframe image 205 generated by the gradation conversion unit 103, and externally selects the output as the output frame image 206. To send.

  Next, details of the processing in step S303 will be described. FIG. 7B is a flowchart showing details of the process in step S303. In step S312, first, the converted gradation control unit 900 refers to the luminance value of each pixel constituting the input frame image 201 and acquires the maximum luminance value Smax. Then, using the acquired maximum luminance value Smax, conversion curves f1 and f2 for converting the luminance value x are defined as follows.

f1 (x) = f2 (x) = x (x ≦ 2Smax−Pmax)
f1 (x) = 2x-2Smax + Pmax (2Smax-Pmax <x)
f2 (x) = 2Smax−Pmax (2Smax−Pmax <x ≦ Smax)
f2 (x) = Pmax (Smax <x)
Here, Pmax is the maximum value that the luminance value can take. For example, when the luminance value is expressed by 8 bits, Pmax is 255. FIGS. 3E and 3F are diagrams showing conversion characteristics of gradation conversion performed by the gradation conversion unit 102 and the gradation conversion unit 103, respectively.

  FIG. 3E shows a conversion characteristic (f1) in the gradation conversion performed by the gradation conversion unit 102, and FIG. 3F shows a conversion characteristic in the gradation conversion performed by the gradation conversion unit 103. (F2) is shown. In FIG. 3E, the horizontal axis represents the input luminance value (input s), and the vertical axis represents the output luminance value (output f1 (s)). On the other hand, in FIG. 3F, the horizontal axis represents the input luminance value (input s) and the vertical axis represents the output luminance value (output f2 (s)). Note that the conversion curves f1 and f2 may be other functions as long as the following conditions are satisfied in order to maintain the gradation of output.

Smax ≦ f1 (Smax) ≦ Pmax
2Smax−Pmax ≦ f2 (Smax) ≦ Smax
FIG. 8C is a diagram illustrating display luminance when the subframe image 203 and the subframe image 205 are combined. In the input luminance range, that is, the luminance value equal to or lower than Smax, the input / output gradations are linearly related, and the gradation can be maintained. Further, when the luminance value is (2Smax−Pmax) or more, a luminance difference is generated between subframes, and a 60 Hz component is generated, so that a feeling of brightness is improved.

  As described above, according to the present embodiment, it is possible to generate a 60 Hz component based on the luminance difference between subframes in a high luminance region within the signal range of the input frame image, and to improve the feeling of brightness. In addition, the gradation can be maintained within the signal range of the input image.

[Fourth Embodiment]
In the first to third embodiments, the case where the frame rate is doubled has been described for the sake of explanation, but the present invention can also be applied to a frame rate of M / N times. FIG. 9 is a diagram illustrating a configuration example when the image processing apparatus according to the first embodiment is expanded to triple the frame rate.

  As described in the first embodiment, when the frame rate is tripled, the frame rate conversion unit 101 generates three subframe images from the input frame image. Therefore, as shown in FIG. 9, it is necessary to provide gradation conversion units 102, 103, and 1401 that perform gradation conversion for each sub-frame image in the subsequent stage of the frame rate conversion unit 101. Of course, the switching unit 104 sequentially selects the gradation conversion units 102, 103, and 1401. FIG. 3C shows a conversion curve for gradation conversion in the gradation conversion unit 102, and FIG. 3D shows a conversion curve for gradation conversion in the gradation conversion units 103 and 1401.

  Further, as shown in FIG. 10, in the configuration shown in FIG. 1A, a high-pass filter 1601 and a low-pass filter 1602 may be provided before the gradation conversion unit 102 and the gradation conversion unit 103, respectively.

  Japanese Patent Laid-Open No. 2002-351382 proposes a frame rate conversion method using a low-pass filter and a high-pass filter. In this case, by suppressing one high spatial frequency of the subframe image and enhancing the high spatial frequency of the other subframe image, motion blur and pseudo contour when the image moves are suppressed. Therefore, in the configuration shown in FIG. 10 as well, pseudo contour and tailing can be reduced in addition to the above-described effect of improving brightness.

  In addition, the techniques described above may be combined as appropriate. Further, in each of the above embodiments, the effect of improving the brightness feeling depending on the flickering state is used, but the flicker feeling and the brightness feeling can be adjusted and set by user input. Specifically, a method of adjusting the f (Smax) of the gradation converting unit while visually checking the display state and setting the curve f according to f (Smax) can be considered.

  According to each of the above embodiments, when a video is displayed, even if the driving frequency is increased by frame rate conversion and the perceived brightness is reduced, a luminance fluctuation having a frequency lower than the output frequency is generated. It becomes possible to improve perceptual brightness. It is also possible to increase the perceived brightness with respect to the physical maximum emission intensity.

[Fifth Embodiment]
The above embodiments have been described on the assumption that all the units included in each of the devices shown in FIGS. 1A, 1B, 1C, 9 and 10 are configured by hardware. However, you may comprise all these parts with a computer program. In this case, a computer having a memory for storing such a computer program and a CPU for executing the computer program stored in the memory can be applied to the image processing apparatus according to each of the above embodiments. .

  FIG. 11 is a block diagram showing a configuration example of computer hardware applicable to the image processing apparatus according to each of the above embodiments. The CPU 1701 controls the entire computer using computer programs and data stored in the RAM 1702 and the ROM 1703, and executes the processes described above as performed by the image processing apparatus according to each of the above embodiments. That is, the CPU 1701 functions as each unit shown in FIGS. 1 (a), (b), (c), 9, and 10.

  The RAM 1702 has an area for temporarily storing computer programs and data loaded from the external storage device 1706, data acquired from the outside via an I / F (interface) 1709, and the like. Further, the RAM 1702 has a work area used when the CPU 1701 executes various processes. That is, the RAM 1702 can provide various areas as appropriate.

  The ROM 1703 stores setting data and a boot program for the computer. The operation unit 1704 is configured by a keyboard, a mouse, and the like, and various instructions can be input to the CPU 1701 by the user of the computer. The display unit 1705 is configured by a CRT, a liquid crystal screen, or the like, and can display a processing result by the CPU 1701 using an image, text, or the like.

  The external storage device 1706 is a large-capacity information storage device represented by a hard disk drive device. The external storage device 1706 stores an OS (operating system) and computer programs for causing the CPU 1701 to realize the functions of the units shown in FIGS. 1A, 1B, 1C, 9 and 10. Yes. Further, each frame image as a processing target may be stored in the external storage device 1706. The external storage device 1706 also stores information (such as coefficients a and b) described as known information in the description of the above embodiments.

  Computer programs and data stored in the external storage device 1706 are appropriately loaded into the RAM 1702 under the control of the CPU 1701 and are processed by the CPU 1701.

  A network such as a LAN or the Internet and other devices can be connected to the I / F 1707, and the computer can acquire and send various information via the I / F 1707. Reference numeral 1708 denotes a bus connecting the above-described units.

[Other Embodiments]
The present invention can also be realized by executing the following processing. That is, software (program) that realizes the functions of the above-described embodiments is supplied to a system or apparatus via a network or various storage media, and a computer (or CPU, MPU, or the like) of the system or apparatus reads the program. It is a process to be executed.

Claims (9)

Obtaining means for sequentially obtaining a plurality of frame images;
Generating means for generating a plurality of sub-frame images from the frame image acquired by the acquiring means;
Conversion means for performing gradation conversion for each of the plurality of subframe images;
Means for sequentially outputting each sub-frame image subjected to gradation conversion by the conversion means,
The converting means includes
In each sub-frame image, the same gradation conversion is applied to pixels whose luminance value is equal to or less than a threshold value,
An image processing apparatus, wherein in each subframe image, gradation conversion different in each subframe image is performed on a pixel having a luminance value larger than a threshold value.   The image processing apparatus according to claim 1, wherein the generation unit generates a plurality of sub-frame images having different gradations from the frame image acquired by the acquisition unit. The converting means includes
When the input luminance value is less than or equal to the threshold value, the change rate of the output luminance value with respect to the input luminance value is configured to be the same in all subframe images, and the input luminance value is larger than the threshold value In this case, the gradation of each of the plurality of subframe images is converted using conversion information configured such that the change rate of the output luminance value with respect to the input luminance value is different in all the subframe images. The image processing apparatus according to claim 1. The converting means includes
The maximum luminance value of the luminance values of each pixel constituting the frame image acquired by the acquisition unit is acquired, and gradation conversion is performed on each of the plurality of subframe images based on the acquired maximum luminance value. The image processing apparatus according to claim 1, wherein the conversion curve is obtained, and gradation conversion is performed based on the obtained conversion curve. Obtaining means for sequentially obtaining a plurality of frame images;
Generating means for generating two sub-frame images from the frame image acquired by the acquiring means;
Filter means for applying a minimum value filter to one subframe image;
Conversion means for performing gradation conversion on the subframe image processed by the filter means;
Means for generating a difference frame image between the other sub-frame image and the sub-frame image converted by the conversion means;
An image processing apparatus comprising: means for sequentially outputting the subframe image converted by the conversion means and the difference frame image. An acquisition step of sequentially acquiring a plurality of frame images;
A generation step of generating a plurality of subframe images from the frame image acquired in the acquisition step;
A conversion step of performing gradation conversion for each of the plurality of subframe images;
And sequentially outputting each sub-frame image that has been subjected to gradation conversion in the conversion step,
In the conversion step,
In each sub-frame image, the same gradation conversion is applied to pixels whose luminance value is equal to or less than a threshold value,
An image processing method, wherein in each subframe image, a gradation conversion different in each subframe image is performed on a pixel having a luminance value larger than a threshold value. An acquisition step of sequentially acquiring a plurality of frame images;
A generating step of generating two sub-frame images from the frame image acquired in the acquiring step;
A filtering step of applying a minimum value filter to one of the subframe images;
A conversion step of performing gradation conversion on the subframe image processed in the filtering step;
Generating a difference frame image between the other subframe image and the converted subframe image in the conversion step;
An image processing method comprising: sequentially outputting the subframe image converted in the conversion step and the difference frame image.   A computer program for causing a computer to function as each unit included in the image processing apparatus according to any one of claims 1 to 5.   A computer-readable storage medium storing the computer program according to claim 8.

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